An adult female Desertas wolf spider carrying her young on her back at Bristol zoo.
Photograph: Bristol Zoo/PA

In what is believed to be a world first, one of the rarest spiders has been bred in captivity at Bristol Zoo Gardens. More than 1,000 Desertas wolf spiderlings, classed as critically endangered, have hatched. Keepers hand-reared some from tiny eggs as they are so precious. At birth, they measure 4mm across, but they will grow to 12cm, with a 4cm body.

The species is found in a single valley on Deserta Grande, one of the Desertas islands near Madeira, Portugal. There are about 4,000 adults left in the wild and it is hoped that some of the spiderlings can be returned to their home.

Mark Bushell, curator of invertebrates at Bristol zoo, travelled to Deserta Grande last year and collected 25 of the spiders to breed. “Because this was the first time this species had ever been taken into captivity to breed, it was a steep learning curve,” he said. “After some of the female spiders were mated, it was an anxious wait to see if they would produce egg sacs. We were thrilled when they did, and to see the tiny spiderlings emerge was fantastic – a real career highlight.”

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The spiders are classified as critically endangered on the International Union for Conservation of Nature (IUCN) red list of threatened species. They are under threat from habitat loss due to invasive grass binding the soil where they burrow and blocking their shelters. Bristol zoo has joined forces with the Instituto das Florestas e Conservação de Natureza and the IUCN to develop a strategy to protect the spiders.

When one of the egg sacs broke, the conservationists carefully transferred the eggs into a miniature incubator. Once they hatched, they were placed in separate containers with sterilised soil, kept in quarantine and individually fed with fruit flies.

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Bristol zoo plans to send hundreds of the spiderlings to zoos across the UK and Europe to set up further breeding points. “Establishing the world’s first captive breeding programme for this species is a fantastic step towards protecting it,” Bushell added. “It is a beautiful and impressive creature, but its natural habitat is being altered by invasive plants.

“There are not enough rocky and sandy areas left for the spiders to burrow and hide in. The spiders are competing for fewer and fewer burrows.”

Horticulture experts from the zoo hope to visit Deserta Grande to begin to restore the original landscape.